Etchant for metal alloy having hafnium and molybdenum

ABSTRACT

An etchant for etching a metal alloy having hafnium and molybdenum includes 20 to 80 percent by weight of nitric acid, 1 to 49 percent by weight of hydrofluoric acid, 1 to 96 percent by weight of sulfuric acid, and 1 to 30 percent by weight of water, based on the total weight of the etchant.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 96146920, filed on Dec. 7, 2007. The entirety theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etchant for metal alloy and anetching method using the etchant, and particularly to an etchant usedfor etching metal alloy having hafnium and molybdenum.

2. Description of Related Art

As the level of integration of integrated circuits increases, thedimensions of semiconductor devices decrease correspondingly. Sincecontact resistance is in opposite proportion to contact area, when thedimensions of transistors in metal oxide semiconductors (MOS) keepshrinking and the dimensions of a device also decrease, the contactresistance thereof increases accordingly such that the drivingcapability of the device is affected. Nowadays, refractory metals,refractory metal nitride and refractory metal oxide have been used inmany researches and studies to replace conventional transistor materialsto serve as conductive layers, dielectric layers and barrier layers.

Molybdenum and hafnium have characteristics of suitable work functions,low resistance and high thermal stability, and are therefore extensivelyapplied in the semiconductor process. In recent years, it is found thatmetal alloy material having hafnium and molybdenum can be applied infabricating N-type channel metal oxide semiconductor (MOS) transistorsand P-type channel metal oxide semiconductor (MOS) transistors. However,no suitable etchant has been found so far that can etch metal alloyhaving hafnium and molybdenum, which has thus limited development ofmetal alloy having hafnium and molybdenum.

SUMMARY OF THE INVENTION

The present invention provides an etchant for etching metal alloy havinghafnium and molybdenum. The etchant is capable of rapidly andeffectively removing a metal alloy material having hafnium andmolybdenum.

The present invention also provides a method of patterning a metal alloymaterial layer having hafnium and molybdenum, suitable for applicationsin the semiconductor process.

The present invention further provides a method of fabricating a gatestructure capable of enhancing the performance of transistors.

The present invention provides an etchant used for etching a metal alloymaterial having hafnium and molybdenum, the etchant comprising at leastnitric acid, hydrofluoric acid and sulfuric acid.

According to an embodiment of the present invention, the etchantcomprises 20-80 percent by weight of nitric acid.

According to an embodiment of the present invention, the etchantcomprises 1-49 percent by weight of hydrofluoric acid.

According to an embodiment of the present invention, the etchantcomprises 1-96 percent by weight of sulfuric acid.

According to an embodiment of the present invention, the metal alloymaterial having hafnium and molybdenum is hafnium-molybdenum alloynitride.

According to an embodiment of the present invention, the metal alloymaterial having hafnium and molybdenum is hafnium-molybdenum alloynitride.

The present invention further provides an etchant used for etching ahafnium-molybdenum alloy nitride. The etchant at least comprises 20-80percent by weight of nitric acid, 1-49 percent by weight of hydrofluoricacid, 1-96 percent by weight of sulfuric acid and 1-30 percent by weightof water.

The etchant of the present invention includes HNO₃, HF, H₂SO₄ and water.The metal alloy having hafnium and molybdenum may be removed and themetal alloy material layer having hafnium and molybdenum may bepatterned with the etchant in different combinations of weight percent.Therefore, in the present invention, the metal alloy having hafnium andmolybdenum with excellent work function, low resistance and high thermalstability can be utilized in fabricating MOS so as to enhanceperformance of transistors.

In order to make the aforementioned and other objects, features andadvantages of the present invention more comprehensible, preferredembodiments accompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIGS. 1A to 1B are schematic cross-sectional views of a process offabricating a patterned metal alloy material layer having hafnium andmolybdenum according to an embodiment of the present invention.

FIGS. 2A through 2D are schematic cross-sectional views illustrating aprocess of fabricating a gate structure according to another embodimentof the present invention.

DESCRIPTION OF EMBODIMENTS

An etchant according to the present invention is suitable for removingmetal alloy having hafnium and molybdenum, such as hafnium-molybdenumalloy nitride. A composition of the etchant includes at least HNO₃, HFand H₂SO₄. In an embodiment, the composition includes 20-80 percent byweight of HNO₃, 1-49 percent of HF, 1-96 percent by weight of H₂SO₄ and1-30 percent by weight of water, based on the total weight of thecomposition. The etchant is capable of completely removing conductivelayers, filler layers or barrier layers using metal alloy having hafniumand molybdenum as a material thereof, for example.

According to an embodiment of the present invention, the etchant of thepresent invention may be used as the etchant to pattern a metal alloymaterial layer having hafnium and molybdenum. A composition of theetchant includes at least HNO₃, HF and H₂SO₄.

FIGS. 1A to 1B are schematic cross-sectional views illustrating aprocess of fabricating a patterned metal alloy material layer havinghafnium and molybdenum according to an embodiment of the presentinvention.

Please refer to FIG. 1. First, a patterned mask layer 104 is formed on ametal alloy material layer 102 having hafnium and molybdenum on asubstrate 100. The substrate 100 is, for example, an insulating materialhaving silicon dioxide, a P-type doped silicon substrate, an N-typedoped silicon substrate, an epitaxial silicon substrate, a galliumarsenide (GaAs) substrate, an indium phosphide (InP) substrate or agermanium silicide (SiGe) substrate. The metal alloy material layer 102having hafnium and molybdenum is, for example, hafnium-molybdenum alloynitride, and a forming method thereof on the substrate 100 is aconventional vapor deposition process. Between the substrate 100 and themetal alloy material layer 102 having hafnium and molybdenum may bedisposed other devices or material layers. However, these other devicesor material layers are not illustrated in the drawings. According to thepresent embodiment of the present invention, the patterned mask layer104 may include a hard mask layer 106 and a photoresist layer 108. Amethod of forming the patterned mask layer 104 may be first depositing ahard mask material layer (not illustrated) by a chemical vapordeposition (CVD) process on the metal alloy material layer 102 havinghafnium and molybdenum, for example. Afterwards, the photoresist layer108 having a predetermined pattern is formed on the hard mask materiallayer. A material of the hard mask material layer is, for example,silicon nitride, amorphous silicon, polysilicon or borophosphosilicateglass (BPSG). According to an embodiment of the present invention, thepredetermined pattern of the photoresist layer 108 is a pattern of aconductive line. According to another embodiment of the presentinvention, a predetermined pattern of the photoresist layer 108 is apattern of a gate. Thereafter, the hard mask material layer is etchedusing the photoresist layer 108 as a mask, so that the predeterminedpattern of the photoresist layer 108 is transferred to the hard maskmaterial layer to form the hard mask layer 106.

Next, referring to FIG. 1B, the patterned mask layer 104 is used as amask layer. The etchant of the present invention is used to perform anetching process 110 on the metal alloy material layer 102 having hafniumand molybdenum to form a patterned metal alloy layer 102 a havinghafnium and molybdenum. A composition of the etchant disclosed by thepresent invention includes at least HNO₃, HF and H₂SO₄. The compositionincludes 20-80 percent by weight of HNO₃, 1-49 percent by weight of HF,1-96 percent by weight of H₂SO₄ and 1-30 percent by weight of water,based on the total weight of the composition. Then, the patterned masklayer 104 is removed by, for example, a wet etching process. Thus, aprocess of patterning the metal alloy material layer 102 having hafniumand molybdenum has been completed.

FIGS. 2A through 2D are schematic cross-sectional views illustrating aprocess of fabricating a gate structure according to another embodimentof the present invention.

Referring to FIG. 2A, a gate dielectric layer 202 is formed on asubstrate 200. The substrate 200 is, for example, a P-type doped siliconsubstrate, an N-type doped silicon substrate, an epitaxial siliconsubstrate, a gallium arsenide (GaAs) substrate, an indium phosphide(InP) substrate or a germanium silicide (SiGe) substrate. A material ofthe gate dielectric layer 202 is hafnium silicon oxynitride, zirconiumsilicon oxynitride or silicon oxide, for example. A method of formingthe gate dielectric layer 202 may be a CVD process or a thermaloxidation process. Next, a metal alloy material layer 204 having hafniumand molybdenum is formed on the gate dielectric layer 202. A method offorming the metal alloy material layer 204 having hafnium and molybdenumis, for example, a physical vapor deposition (PVD) process or a CVDprocess.

Please refer to both FIGS. 2A and 2B. Afterwards, the metal alloymaterial layer 204 having hafnium and molybdenum is patterned to form apatterned metal alloy layer 204 a having hafnium and molybdenum. Themetal alloy material layer 204 is patterned, for example, by forming apatterned mask layer 205 on the metal alloy material layer 204 havinghafnium and molybdenum and etching the metal alloy material layer 204having hafnium and molybdenum with the etchant and the patterned masklayer 205 as a mask. Please refer to the description in the previousembodiment for a forming method and a material of the patterned mask205, and a description thereof is thus omitted herein. A composition ofthe etchant used herein includes at least HNO₃, HF and H₂SO₄. Thecomposition includes 20-80 percent by weight of HNO₃, 1-49 percent byweight of HF, 1-96 percent by weight of H₂SO₄ and 1-30 percent by weightof water, based on the total weight of the composition.

Thereafter, please refer to FIGS. 2B and 2C simultaneously. A pull-backprocess is optionally performed on sidewalls 207 of the metal alloylayer 204 a having hafnium and molybdenum with the same etchant so thateach side of the metal alloy layer 204 a having hafnium and molybdenumis pulled inward a distance d to form a gate 204 b. A temperature rangeof the etchant is 1-100° C. It should be noted that during the pull-backprocess, the metal alloy material remaining on the substrate 200 wouldalso be removed, and thereby avoiding bridges derived from the metalalloy material having hafnium and molybdenum.

Afterwards, referring to FIG. 2D, the patterned mask layer 205 isremoved. A method of removing the patterned mask layer 205 may be a wetetching process, a dry etching process or both wet and dry etchingprocesses.

In summary, the composition of the etchant disclosed in the presentinvention includes at least HNO₃, HF, H₂SO₄ and water. With differentpercent by weight concentration combinations, the etchant can etch themetal alloy material having hafnium and molybdenum and pattern the metalalloy material layer having hafnium and molybdenum, so that the metalalloy material having hafnium and molybdenum may be applied in theprocess of MOS transistors. For example, the etchant may be used to formdevices in the transistor such as conductive lines and gates whichrequire conductive materials such that the advantages of metal alloyhaving hafnium and molybdenum, such as excellent work functions, lowresistance and high thermal stability, may be well utilized to enhancethe performance of the transistor.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the presentinvention. In view of the foregoing, it is intended that the presentinvention cover modifications and variations of this invention providedthey fall within the scope of the following claims and theirequivalents.

1. An etchant used for etching a metal alloy material having hafnium andmolybdenum, the etchant comprising at least nitric acid, hydrofluoricacid and sulfuric acid.
 2. The etchant as claimed in claim 1, whereinthe etchant comprises 20-80 percent by weight of nitric acid.
 3. Theetchant as claimed in claim 2, wherein the etchant comprises 1-49percent by weight of hydrofluoric acid.
 4. The etchant as claimed inclaim 3, wherein the etchant comprises 1-96 percent by weight ofsulfuric acid.
 5. The etchant as claimed in claim 4, wherein the metalalloy material having hafnium and molybdenum is hafnium-molybdenum alloynitride.
 6. The etchant as claimed in claim 1, wherein the metal alloymaterial having hafnium and molybdenum is hafnium-molybdenum alloynitride.
 7. An etchant used for etching a hafnium-molybdenum alloynitride, at least comprising: nitric acid, 20-80 percent by weight;hydrofluoric acid, 1-49 percent by weight; sulfuric acid, 1-96 percentby weight; and water, 1-30 percent by weight.